Abstract : This study is one part of a program of research with regard to the repair of composite structure with extern bonded-patches. The principal objectives of this program are, on one side, the identification of all the factors susceptible to influence the long-term performance of this type of repair, on the other, to determine the extent to which the use of such assemblage can be proved to be an optimal solution. The conception of such a system needs essentially the development of a tool of simulation and of robust prediction because various mechanisms of damage can take place in a very complex way and the final fracture of the system arise from the propagation of damage zones. This study consists of both numerical simulation and experimental aspect which can help us, on one side, understand the mechanisms of damage and its evolution in a repair structure, on the other, valid the numerical model. In particular, we concentrate in the application of cohesive zone model using LS-dyna. The behavior of delamination of carbon-epoxy composite and the adhesive is studied with the experiments in mode I, mode II and mode mixed. A parametric study is carried out. The validated cohesive zone model is used to simulate the tensile behavior of composite repaired by extern bonded-patches